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Discussion Starter #1
G'day all, I've recently rebuilt my '84 LWB 2.8L petrol as it had blown the head gasket and warped the head. I replaced it with the P90 head which is supposedly meant for a turbo'd engine as it has a larger combustion chamber and I was told that it might lower the compression on a non-turbo motor. It cranks over no worries but will not start. I've had it compression tested which came to 25 (apparently supposed to be 125) and also been told it might be an ignition and/or valve timing problem. I'm desperately try to get her going again so I'm just wondering if anyone has done the same head swap and the problems/solutions that you have had, or if anyone has any helpful information then it would be greatly appreciated. Cheers, centra.
 

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According to this website your compression dropt to 7.275 so maybe that is not enough to start? I would get rid of the head cause lower compression means less Hp and torque in a N/A setup.

Engine Design Utility
 

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yer sounds like your static compression is heaps low, and your dynamic compression is even worse. the dynamic is taking into account valve positions, hence the low compression test results.

have you checked everything is working correctly, ie cam and dizzy are dialled correctly, carby is all good, leads are in correct order etc.

you could probably feed it some serious boost at those compression levels!
 

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Discussion Starter #4
Thanks for the replies guys. That website's pretty handy.. neRok I will triple check over everything to make sure it's all in tune. If I did want to chuck a turbo on it would i need to change the pistons or anything else? And would it raise the compression enough to actually start?
 

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it wouldnt raise the compression at all at idle, coz the turbo wouldnt be operating (runs on exhaust gas, no exhaust gas if its not running).
and you can turbo any engine without changing anything. but how long it will last is a different question!
 

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Id be checking EVERYTHING first before worrying about the comp ratio
As mentioned , is everything set correctly ???
Do a few checks ect ,before being disheartened about it
The P90 heads are the ducks guts in the L28s
But there are to many variables (and lacking info) to determine anything
 

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I agree with MQ mad. I would be inclined to think that the problem is in the setup of the timming chain. There are many motors running the p90 heads carby and fuel injection.

Did you use a wedge on the timming chain, or did you pulled the front off and do the job properly. The first motor I done, I used a block of wood to hold the chain while I pulled the head off. It was not in the correct place and the chain tensioner poped out.

If the timming is not correctly set up, the motor will not run.

Also if you have the dissy is 180 out, the motor will back fire though the carby.
 

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Even the Nissan manual tells you to use a wedge for the timing chain.

The engine will run whit this head but will make less Hp and Torque.
 

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HHHMMM,
I wonder how a good RB30 would go against a good L28

With all things equal of course

Injected Vs injected ect ect

I dont think the L28 would shy away from a good battle
 

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HHHMMM,
I wonder how a good RB30 would go against a good L28

With all things equal of course

Injected Vs injected ect ect

I dont think the L28 would shy away from a good battle
thats not equal, L28 would of had heaps of coin thrown at it, RB30 would be stock. its like saying 'i wonder if i stroke my 308 holden to 355, will it beat a 5.7 gen 3'. probably, but it would cost a packet, and if gen 3 had same packet spent on it, bye-bye 355.

edit- it just occured to me that 280zx have factory efi. i thought you were talking all custom work making a carby l28 into efi lol. it may be a close battle, but i think rb30 would be winner in outright power. though they probably make their power with higher RPM (cant say, havent seen some dyno sheets). i would prefer a more meaty mid-range in a 4wd, if L28 had that over the RB30 then i would personally keep L28 and spend money on it, rather than spending money getting a RB30 in the bay.
actually, if i had L28 MQ, i would chuck the 253 in it thats sitting in my carport :cool:
 

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Sorry about the thread hi-jack.

It will be bulk standard carby l28 compared against a bulk standard carby Gq RB30.

The RB30 has cost me the same as my last l28- $100 so I should end up with a bit more go go.
 

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There was a bloke on here a while ago who was running an EFI L28 in a patrol
This was a freakin power house

As i mentioned both stock Vs stock im just wondering how the L28 would go against the RB30
Just curious
 

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Discussion Starter #15
update! after the re-doing the timing and a bit of tuning she's got her rumble back! does lack a bit of power as expected but i'm keen to turbo it if it's not too much of a hassle.. what parts are compatible for a turbo conversion? cheers for the help guys!
 
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